1. Field of the Invention
The present invention relates to a polarized electromagnetic actuator device, and more particularly to such a device advantageous for operating relay contacts in a single-stable manner.
2. Description of the Prior Art
Prior polarized electromagnetic actuators for relays are known such as disclosed in U.S. Pat. Nos. 4,064,471 and 4,134,090 and in German Patent Publication (Auslegeschrift) No. 2,148,377, in which a permanent magnet is combined with an electromagnet to provide a magnetic system utilized for obtaining a single-stable relay operation. As shown in FIG. 1 of the attached drawing of the present invention which is a greatly schematic representation of the prior magnetic system, the prior devices include a slightly V-shaped armature 6 carrying one or more movable contacts and pivotally supported for angular movement in relation to the electromagnet 1 with a yoke 2 and an exciter coil 5. The permanent magnet 7, which is incorporated for the purpose of biasing the armature 6 to a reset position and holding the same in the position, is coupled to the electromagnet 1 with its one pole end connected to one of the yoke legs 3 and with other pole end away from the other yoke leg 4 but in closely adjacent relation to the pivot axis of the armature 6. The permanent magnet 7 thus incorporated forms two separate magnetic flux paths, one being a reset flux path circulating from the permanent magnet 7 and extending only through one end portion of the armature 6 as indicated by a line A with arrows and the other being a set flux path circulating from the same and extending through the entire length of the yoke 2 as indicated by a line B with arrows of the figure. In this way, the reset flux path A is made far shorter than the set flux path B by the length of the yoke 2 to thereby exert a magnetomotive force stronger than the set flux path, magnetically biasing the armature 6 to the reset position. That is, the prior devices depend upon the difference in the length or the magnetic resistance between the first and second flux paths A and B for biasing the armature to the reset position. However, such difference is closely related to the configurations of the components constructing the device and is therefore susceptible to dimensional variations thereof, making it rather difficult to provide the device of consistent magnetic characteristics. This is most disadvantageous in designing the relay of single-stable operation by combining the device with suitable return spring means biasing the armature from the set position to the reset position. The above problem is especially serious when the actuator device or the relay assembled therefrom is needed for miniaturization where the armature is driven to move between the set and, reset positions by a delicate difference in the combination forces applied thereto from the magnetic circuit and the return spring means.